Chronic synchronized atrial-ventricular pacing has been shown to improve symptoms and effort tolerance in patients with obstructive hypertrophic cardiomyopathy, changes associated with reduction in left ventricular outflow gradient. To assess the impact of atrial-ventricular pacing in non-obstructive hypertrophic cardiomyopathy, 6 patients underwent exercise hemodynamic studies before and 1 to 6 months following implantation of a pacemaker programmed to synchronized atrial ventricular pacing. All patients improved by at least 1 functional class, and significantly increased Bruce protocol treadmill exercise duration by 2.5 minutes. During semi-erect bicycle ergometry, there was a significant reduction in the left ventricular filling pressures during exercise by 9 mmHg without compromise to the cardiac output or blood pressure response to exercise. Thus, chronic atrial-ventricular pacing benefits symptoms and exercise capacity of patients with non-obstructive hypertrophic cardiomyopathy with reduction in exercise related left ventricular filling pressures, possibly due to pacemaker-mediated dysynchronous left ventricular contraction with reduction in myocardial oxygen demands and less ischemia during stress.